Restenosis remains the most significant clinical challenge limiting the success of angioplasty and/or stenting. Neointimal hyperplasia is the primary reason for in-stent restenosis. The objective of this proposal is to use variations among mouse strains in injury-induced neointimal hyperplasia to identify genetic factors that contribute to the development of post-angioplasty/stent restenosis. On the apolipoprotein E-deficient (apoE-/-) background, inbred mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) differ markedly in injury-induced neointimal hyperplasia. B6.apoE-/- mice readily develop neointimal hyperplasia whereas CSH.apoE-/- mice are totally resistant to lesion formation despite the fact that the two strains have comparable hyperlipidemia on a chow diet. The F1 hybrids are intermediate in the phenotype, indicating a codominant control of the phenotype in the mice. Immediately following arterial injury is deposition of a layer of platelets at sites of vascular injury. Subsequently, leukocyte recruitment and infiltration occur. Recruited macrophages and lymphocytes and damaged endothelial cells and vascular smooth muscle cells (SMC) release cytokines, growth factors, and matrix metalloproteinases (MMP) that stimulate SMC in the medial wall to proliferate and migrate into the damaged intima. We hypothesize that genetic factors that influence the induction of cytokines and growth factors or that modulate the proliferation of vascular smooth muscle cells contribute to the variation in neointimal hyperplasia of the two strains. To test this hypothesis, B6.apoE-/- mice will be mated with CSH.apoE-/- mice to generate F1 mice, which will be subsequently intercrossed to generate a cohort of F2 mice. The male F2 mice, together with male F1 and two parental strains, will be subject to endothelial denudation of the left common carotid artery. Neointimal thickening will be quantitated by light microscopy. Blood will be collected for assessment of fasting lipid and inflammatory marker levels. Genome-wide scans will be performed using microsatellite markers to define the genetic loci that are linked to differences in the phenotypes between B6 and C3H strains. After the genome screen has detected chromosomal regions that show linkage with neointimal lesions, we will type additional closely spaced polymorphic markers to narrow the regions. One to two major QTLs for neointimal hyperplasia will be dissected through construction and analysis of congenic strains.